The intertidal rocky shore

identifying red seaweeds of the intertidal rocky shore

By Dr J Floor Anthoni (2007)
www.seafriends.org.nz/enviro/rsred.htm

Red seaweeds are most suited to grow in dark
places and in the deep. Yet many species survive well near the surface
and in rock pools of the intertidal rocky shore. It is difficult to tell
the various species apart. Many red seaweeds are intrically branched, forming
beautiful patterns when spread out over a white page of paper.

red seaweedsRed seaweeds have a red pigment that absorbs blue light,
which penetrates deepest in the sea. As a result, red seaweeds can be found
deeper than brown and green seaweeds. But even in the sunlit shallows of
the rocky shore, one can find a number of species. The red seaweeds comprise
the largest number of seaweeds in New Zealand.

(Porphyra columbina) [karenga] looks like tissue paper.
It flourishes in winter and spring. Small plants fold like a rosette.

Apophlaea sinclaiirii is a dull brown-red rubbery
alga that grows flat over the rock or extends tiny rubbery fingers. It
dries rigid and black like tar but swells when the tide is in.

Apophlaea lyalli grows up to 18cm on high tidal rocks
of the southern South Island. Branches rounded, dark red and bushy with
firm texture.

f034114: the finely branched Pterocladia lucida branches
in a flat plane. From this seaweed the agar gelatine is made. Agar is used
as a stiffener in foodstuffs, toothpaste, soaps, shampoos etc. It is also
used scientifically to grow bacteria on.

0910044: Pterocladia capillacea is a creeping
alga with thin stems with tufted branches. It prefers to live under water.
This seaweed is also suitable for making agar.

Plocamium microcladioides (up to 15cm) has firm cylidrical
stipes that branch in one plane. Terminal hook-like branches in sets of
three on the same side of the blade. Lower intertidal.

Polysiphonia decipiens is the most commonly found
of this genus. It is highly branched with no obvious stipe and covered
with pigmented hairs. It has a soft texture and dark red-brown colour and
sometimes grows on brown seaweeds.

Rhodymenia novazelandica has a fine, open fan shape,
branching dichotomously in one plane. Red.

f051727: a hard red seaweed growing out from a central
clump (Apophlaea sinclairii).

f051729: finely branching (Plocamium costatum)
in the background. In the foreground Melanthalia abscissa?

f051725: (Callophyllis variegata?).

f051728: ?

f051229: ?

f051211: the fretsaw weed (Vidalia colensoi, Osmundaria
c.) with alternating teeth is found in robust wave action. It does
not feel slimy but rough and can grow to dense patches. North Island.

f222613: Pachymenia lusoria has long flat blades that
look green, sprouting from thin stipes clustered from a single holdfast.
Blades have jagged edges. West coast of the North Island and South Island
but rare in central NZ.

the prickly weeds (Echinothamnion spp.) have
regularly branching, bushy and shaggy branches of unequal length. Reddish
brown, sometimes growing on other seaweeds. Southern half of NI, all of
SI.

f048222: a healthy seaweed garden at the Poor Knights islands
shows a high variety of seaweeds against a backdrop of an Ecklonia
kelp forest. From left to right: stalked kelp (Ecklonia radiata),
hugged by strap kelp (Lessonia variegata) and beneath it pink paint.
The red seaweeds are (Rhodophyllis membranacea?) and the broader
leafed (?). The tall bladderweed looks like the featherweed (Carpophyllum
plumosum) but is in fact (Cystophora platylobium). Such seaweed
gardens can be found inside large rock pools.

f210512: an exposed South Island rock pool shows the dominant
species. From left to right: the sheltered form of bullkelp (Durvillea
antarctica), the long strings of giant kelp (Macrocystis pyrifera),
the hardy cartilage weed (Xiphophora gladiata) and in the middle
of the water the spiky-leafed (Echinothamnion sp.?).

f027103: a fine example of a semi-sheltered shore near Dunedin:
From left to right: the giant kelp (Macrocystis pyrifera)
with its thin leaves, the branching bullkelp (Durvillea willana),
the hardy cartilage weed (Xiphophora gladiata) and the featherweed
(Carpophyllum
plumosum).